This invention relates to a magnetic head employed for high-density recording of speech signals, picture signals or information signals, as magnetic signals, on a recording track of a magnetic recording medium, such as a magnetic tape, in e.g., a video tape recorder (VTR), a digital audio tape recorder (DAT) or a digital data recording device, with high recording density. The invention also relates to a magnetic material for a magnetic head employed therein.
A magnetic recording and/or reproducing apparatus, such as VTR or DAT, employing a magnetic recording tape or the like as a magnetic recording medium, has a magnetic head for reading out or reproducing information signals from a signal recording surface of the magnetic recording tape, and/or writing or recording information signals on the signal recording surface, for reading and/or recording the information signals on or from the magnetic recording medium.
The magnetic head includes a magnetic core and a member wound thereon, such as a coil. A magnetic gap, which is a small interstice, is formed in the magnetic core. The coil plays the role of transmitting information signals as magnetic flux to the magnetic core for recording or reproduction.
On the other hand, the magnetic core plays the role of transmitting the magnetic flux from the coil to the magnetic recording medium and vice versa for recording and reproduction, respectively. The magnetic gap acts for limiting the spreading of the magnetic field for recording information signals, while acting as a magnetic flux intake opening from the magnetic recording medium during reproduction.
Recently, the tendency is towards recording or reproducing signals of shorter wavelengths for recording or reproducing more information signals with a view to improving the quality of picture signals to be recorded or reproduced, or to increasing the storage capacity. To this end, a high coercivity magnetic recording medium, such as a metal tape in which magnetic metal powders, that is magnetic powders employed for a magnetic layer of the magnetic recording medium, are coated on a base film, or a vaporized tape, in which a magnetic metal material is directly deposited on the base film by vapor deposition, is being used in increasing numbers.
For enabling recording or reproduction on or from such high coercivity magnetic recording medium, proposals have been made of a layered magnetic head in which a magnetic layer of a metal having high magnetic permeability and high saturation flux density, such as iron-based alloy, iron-nickel based alloy or an iron-cobalt based alloy, is used as a magnetic core material for a magnetic head, or a so-called metal-in-gap (MIG) magnetic head.
The layered magnetic head has magnetic core halves each formed by a magnetic metal layer sandwiched between a pair of guard pieces. The magnetic core halves are abutted to each other and unified together by glass fusion to complete a unified structure of the magnetic head.
The present inventors have proposed such a layered magnetic head in which magnetic metal films constituting the magnetic core are magneto-statically connected to each other at both ends for improving the efficiency of the magnetic head especially in a high frequency range.
With the above-described layered magnetic head employing the magnetic metal material for the magnetic core material for effecting high-density recording, since the magnetic metal layer is worn out more severely than the non-magnetic guard material by contact with the magnetic tape, the magnetic metal layer of the magnetic core is worn out more quickly than other portions, as a result of which the magnetic core portion is receded due to partial abrasion. With the layered magnetic head, there is generated an interstice between the magnetic gap and the magnetic recording medium, and the magnetic field intensity of the magnetic gap with respect to the magnetic recording medium is lowered, so that the electro-magnetic conversion characteristics are lowered especially in the high frequency range.
Such partial abrasion may be diminished by employing a magnetic metal layer-guard material combination exhibiting similar values of the amount of wear with respect to the magnetic tape. However, there lacks up to now a magnetic metal material having abrasion resistance affording practically acceptable durability of the magnetic head and sufficient magnetic properties. For this reason, if the partial abrasion is to be diminished, one has to select a guard material having a significant amount of abrasion with respect to the magnetic recording medium in order to match the properties of the guard material to those of the magnetic core material. If, solely in this consideration, a guard material having significant amount of wear with respect to the magnetic tape is selected, the resulting magnetic head is poor in durability since it exhibits significant abrasion by contact with the magnetic tape, even although it undergoes only little partial abrasion.
Thus an MnO-NiO based non-magnetic material as disclosed in U. S. Pat. Nos. 4,805,059 or 5,057,374 and in JP Patent Kokai Publication JP-A-2-296765, or a CaO-TiO.sub.2 -NiO non-magnet material, as disclosed in JP Patent Publication JP-B-3-45024 or JP patent Kokai Publication JP-A-6-28807, have been proposed as a non-magnetic material for a magnetic head.
The MnO-NiO based non-magnetic material, while having a thermal expansion coefficient comparable with the magnetic metal film, has a significant value of abrasion with respect to the magnetic tape.
On the other hand, the CaO-TiO.sub.2 -NiO non-magnet material, as disclosed in JP Patent Publication JP-B-3-45024, is composed of 3 to 35 mol % of CaO, 3 to 30 mol % of TiO.sub.2 and 60 to 90 mol % of NiO, has a thermal expansion coefficient comparable to the magnetic metal film, and exhibits an extremely small value of abrasion with respect to the magnetic tape. However, the nonmagnetic material suffers from a significant difference in the amount of wear from that of the magnetic metal film with respect to the magnetic tape, that is partial abrasion.